This invention relates to electronic flash devices, and, more particularly, to an actuating circuit for a light measuring circuit of the electronic flash device.
It is well known to provide an electronic flash device of the so-called computer type in which the reflected light from an object illuminated by the flash tube is sensed and the time duration of firing of the flash tube is controlled in accordance with the sensed light quantity.
Such computer type electronic flash device, however, when put into a lighting situation where the object to be photographed is surrounded by many photographers, or in a somewhat bright room, tends to initiate an operation of the light measuring circuit before the firing circuit is actuated. This makes it impossible not only to obtain the desired amount of flash light, but also in some cases to actuate the firing circuit.
To avoid this, according to the prior art, a capacitor is provided for supplying a driving voltage to the actuation control input of the light measuring circuit when the firing of the flash tube is initiated to thereby insure that at the same time when the flash light is emitted, the light measuring circuit starts to operate.
Another major problem in the conventional electronic flash device is that, as the flash tube is successively fired with very large consumption of electrical energy of the electrical power source or battery, the resultant voltage on the battery, though not insufficient for normal operation of the other circuit portions, is no longer effective to charge the main capacitor to the critical voltage level for the firing of the flash tube.
Indeed, this problem is solved by using an auxiliary capacitor also arranged to be connected in series to the main capacitor when the trigger switch is closed, whereby the sum of the voltages across the main capacitor and auxiliary capacitor is applied across the flash tube at the time of triggering of the flash tube.
Since the above-described two major problems in the conventional computer type electronic flash device have thus been solved, the use of the individual capacitors for the solution of the respective problems at a time gives rise to an alternative drawback that the complexity of the device is increased, the desired compactness is not achieved, and high cost of manufacture results.